Time resolved spectroscopic investigation of SiD2 + D2: kinetic study

Silylenes (silanediyls) have made an important impact on organosilicon chemistry even if it is of more recent foundation than carbenes in organic chemistry and much less complete. These species are highly reactive intermediates. They play a central role in the chemical vapour deposition (CVD) of various silicon-containing thin films which have a technological importance in microelectronics as well as in the dry etching processes of silicon wafers. Spectroscopic methods have been developed to observe these species, a necessary pre-requisite to their direct monitoring. In this work, deuterated phenylsilane precursor, PhSiD3 was chosen for SiD2 because its analogue phenylsilane, PhSiH3 proved to be a good precursor for SiH2 and the high quality decay signals observed revealed that SiD2 be readily detected from PhSiD3 and that if other decomposition pathways (e.g. PhSiD + D2) are occurring, they do not effect measurements of the rate constants for SiD2. The absorption spectrum of SiD2 formed from the flash photolysis of a mixture of PhSiD3 and SF6 at 193nm were found in the region 17384-17391 cm-1 with strong band at 17387.07 cm-1. This single rotational line of pQ1 was chosen to monitor SiD2 removal. Time-resolved studies of SiD2 have been carried out to obtain rate constants for its bimolecular reactions with D2. The reactions were studied over the pressure range 5-100 Torr (in SF6 bath gas) at four temperatures in the range 298-498K. Single decay from 10 photolysis laser shots were averaged and found to give reasonable first-order kinetics fits. Second order kinetics were obtained by pressure dependence of the pseudo first order decay constants and substance D2 pressures within experimental error. The reaction was found to be weakly pressure dependent at all temperatures, consistent with a third-body mediated association process. In addition, SiH2+ H2 reaction is approximately ca. 60% faster than SiD2+D2 reaction. Theoretical extrapolations (using Lindemann-Hinshelwood model and Rice, Ramsperger, Kassel and Marcus (RRKM) theory) were also carried out and obtained data fitted the Arrhenius equations

The statistical distribution of money and the rate of money transference

The distribution of money is analysed in connection with the Boltzmann distribution of energy in the degenerate states of molecules. Plots of the population density of income distribution for various countries are well reproduced by a Gamma function, confirming the validity of the statistical distribution at equilibrium. The equilibrium state is reached through pair wise money transference processes, independently of the shape of the initial distribution and also of the detailed nature of the money transactions between the economic agents.Comment: 15 pages plus 1 table plus 3 figure

Theoretical and experimental study of tropylium formation from substituted benzylpyridinium species

Fragmentation pathways of unsubstituted and substituted benzylpyridinium compounds were investigated using mass-analysed kinetic energy (MIKE) technique in combination with high level of quantum chemical calculations in the gas phase. Fast atom bombardment (FAB) source was used for ionisation of the studied compounds. The formation of both benzylium and tropylium species were investigated. Hybrid Hartree-Fock/Density Functional Theory calculations have been performed to assess the geometries and the energies of the transition states and intermediates. For each cases, different reaction pathways were investigated, and particularly in the case of the formation of tropylium species, the formation of the seven-membered ring before or after the loss of pyridine were studied. The effect of para-methyl and para-methoxy substituents on the activation energy of the rearrangement process to form thermodynamically stable tropylium compounds has been studied. Theoretical calculations showed competition between direct bond cleavage and rearrangement reactions to form benzylium and tropylium compounds, respectively. Experimental results also suggested that the rearrangement process takes place to yield stable tropylium under “soft ionisation techniques”, such as FAB